In this kind of planar light emitting devices, a transparent conductive film can be used as a planar anode, and a metal membrane can be used as a planar cathode. In order to activate such a device at high brightness, it is necessary to supply the device with a larger electric current. However, the sheet resistance of the planar anode is higher than that of the planar cathode, and therefore an electric potential gradient becomes large in the planar anode, and a large voltage is applied to a light emitting layer between the planar anode and the planar cathode. As a result, the device possesses a large dispersion in brightness.
This problem can be solved with, for example, an organic EL element (an organic electroluminescence device) disclosed in Japanese Patent Application Publication Number P2008-123882A published on May 29, 2008. This element is composed of a pair of opposite electrodes and an organic EL layer which includes at least an organic emitting layer and intervenes between the electrodes.
Specifically, a transparent electrode is formed on an insulation substrate with translucency, and a non-luminous insulation layer arranged in a pattern is formed in a required region of a surface of the transparent electrode. An organic EL layer containing organic light emitting material is then formed on the transparent electrode and the non-luminous insulation layer to coat them. An opposite electrode opposed to the transparent electrode is then formed on the organic EL layer. The whole light emitting part is then airtight sealed with a seal member made of glass or stainless steel.
Thus, by using the non-luminous insulation layer, when the device is activated under a drive condition by which average brightness becomes 1000 cd/m2, brightness uniformity is reduced.
However, the area expansion of the light emitting part is limited due to increase of the area of the non-light emitting part, because the transparent electrode is connected to a power source through an electrode terminal located at an opposite edge of the insulation substrate with translucency, while the opposite electrode is connected to the power source through an electrode terminal located at another opposite edge of the insulation substrate with translucency. If a plurality of organic EL elements is arranged, a distance between adjacent light emitting parts becomes large, thereby causing disfigurement.